This loader delays the compilation of specified PSGI application until the first request time. This prevents bad things from happening with preforking web servers like Starlet, when your application manipulates resources such as sockets or database connections in the master startup process and then shared by children.

You can combine this loader with -M command line option, like:

plackup -s Starlet -MCatalyst -L Delayed myapp.psgi

loads the module Catalyst in the master process for the better process management with copy-on-write, however the application myapp.psgi is loaded per children.

Starman since version 0.2000 loads this loader by default unless you specify the command line option --preload-app for the starman executable.